Anthracyclines are antibiotic compounds that exhibit cytotoxic activity. Studies have indicated that anthracyclines may operate to kill cells by a number of different mechanisms including: 1) intercalation of the drug molecules into the DNA of the cell thereby inhibiting DNA-dependent nucleic acid synthesis; 2) production by the drug of free radicals which then react with cellular macromolecules to cause damage to the cells or 3) interactions of the drug molecules with the cell membrane [see, e.g., C. Peterson et al., “Transport And Storage Of Anthracycline In Experimental Systems And Human Leukemia” in Anthracycline Antibiotics In Cancer Therapy; N. R. Bachur, “Free Radical Damage” id. at pp. 97-102]. Because of their cytotoxic potential anthracyclines have been used in the treatment of numerous cancers such as leukemia, breast carcinoma, lung carcinoma, ovarian adenocarcinoma and sarcomas [see e.g., P. H—Wiernik, in Anthracycline: Current Status And New Developments p 11]. Commonly used anthracyclines include doxorubicin, epirubicin, idarubicin and daunomycin.
In the recent years many new highly cytotoxic anthracyclines have been synthesized. For example nemorubicin, the anthracycline derivative bearing a substituted morpholino ring linked to the C-3′ position of the sugar moiety has shown promising antitumor activity on experimental murine tumors [see: J. W. Lown, Bioactive Molecules (1988) vol 6:55-101] and is currently under clinical phase trials for the treatment of hepatocellular carcinoma [see: C. Sessa, O. Valota, C. Geroni, Cardiovascular Toxicology (2007) 7(2):75-79]. Although these compounds may be useful in the treatment of neoplasm and other disease states wherein a selected cell population is sought to be eliminated, their therapeutic efficacy is often limited by the dose-dependent toxicity associated with their administration.
Attempts to improve the therapeutic effect of these compounds have been tried by linking the anthracycline to antibodies or to different carriers. An example of an anthracycline conjugated with antibodies is reported, for example, in EP 0328147 to Bristol Myers, in WO 9202255 to Farmitalia Carlo Erba or in U.S. Pat. No. 5,776,458 to Pharmacia & Upjohn.
Other interesting tricyclic morpholino anthracycline derivatives, characterized by high activity, were described and claimed in the International patent application WO 98/02446 (1997) of M. Caruso et al. Among these derivatives, a particularly active compound is PNU-159682, described by Quintieri, L., Geroni, C. et al. in Clinical Cancer Research (2005) 11(4):1608-1617. Compound PNU-159682 has the formula (IIA) as defined herein below, and the following chemical names:    5,12-naphthacenedione, 7,8,9,10-tetrahydro-6,8,11-trihydroxy-8-(hydroxyacetyl)-1-methoxy-10-[[(1S,3R,4aS,9S,9aR,10aS)-octahydro-9-methoxy-1-methyl-1H-pyrano[4′,3′:4,5]oxazolo[2,3-c][1,4]oxazin-3-yl]oxy]-, (8S,10S)-(9CI);    5,12-naphthacenedione, 7,8,9,10-tetrahydro-6,8,11-trihydroxy-8-(hydroxyacetyl)-1-methoxy-10-[(octahydro-9-methoxy-1-methyl-1H-pyrano[4′,3′:4,5]oxazolo[2,3-c][1,4]oxazin-3-yl)oxy]-, [1S-[1α,3β(8R*,10R*), 4aβ,9α,9aα, 10aβ]] or (8S,10S)-6,8,1,1-trihydroxy-8-(hydroxyacetyl)-1-methoxy-10-{[(1S,3R,4aS,9S,9aR,10aS)-9-methoxy-1-methyloctahydro-1H-pyrano[4′,3′:4,5][1,3]oxazolo[2,3-c][1,4]oxazin-3-yl]oxy}-7,8,9,10-tetrahydrotetracene-5,12-dione.
Antibody therapy has been established for the targeted treatment of patients with cancer, immunological and angiogenic disorders (Carter, P. (2006) Nature Reviews Immunology 6:343-357). The use of antibody-drug conjugates (ADC), i.e. immunoconjugates, for the local delivery of cytotoxic or cytostatic agents, i.e. drugs to kill or inhibit tumor cells in the treatment of cancer, targets delivery of the drug moiety to tumors, and intracellular accumulation therein, whereas systemic administration of these unconjugated drug agents may result in unacceptable levels of toxicity to normal cells as well as the tumor cells sought to be eliminated (Xie et al (2006) Expert. Opin. Biol. Ther. 6(3):281-291; Kovtun et al (2006) Cancer Res. 66(6):3214-3121; Law et al (2006) Cancer Res. 66(4):2328-2337; Wu et al (2005) Nature Biotech. 23(9):1137-1145; Lambert J. (2005) Current Opin. in Pharmacol. 5:543-549; Hamann P. (2005) Expert Opin. Ther. Patents 15(9):1087-1103; Payne, G. (2003) Cancer Cell 3:207-212; Trail et al (2003) Cancer Immunol. Immunother. 52:328-337; Syrigos and Epenetos (1999) Anticancer Research 19:605-614). Maximal efficacy with minimal toxicity is sought thereby. Efforts to design and refine ADC have focused on the selectivity of monoclonal antibodies (mAbs) as well as drug mechanism of action, drug-linking, drug/antibody ratio (loading), and drug-releasing properties (McDonagh (2006) Protein Eng. Design & Sel.; Doronina et al (2006) Bioconj. Chem. 17:114-124; Erickson et al (2006) Cancer Res. 66(8):1-8; Sanderson et al (2005) Clin. Cancer Res. 11:843-852; Jeffrey et al (2005) J. Med. Chem. 48:1344-1358; Hamblett et al (2004) Clin. Cancer Res. 10:7063-7070). Drug moieties may impart their cytotoxic and cytostatic effects by mechanisms including tubulin binding, DNA binding, or topoisomerase inhibition. Some cytotoxic drugs tend to be inactive or less active when conjugated to large antibodies or protein receptor ligands.
The anthracycline analog, doxorubicin (ADRIAMYCIN®) is thought to interact with DNA by intercalation and inhibition of the progression of the enzyme topoisomerase II, which unwinds DNA for transcription. Doxorubicin stabilizes the topoisomerase II complex after it has broken the DNA chain for replication, preventing the DNA double helix from being resealed and thereby stopping the process of replication. Doxorubicin and daunorubicin (DAUNOMYCIN) are prototype cytotoxic natural product anthracycline chemotherapeutics (Sessa et al (2007) Cardiovasc. Toxicol. 7:75-79). Immunoconjugates and prodrugs of daunorubicin and doxorubicin have been prepared and studied (Kratz et al (2006) Current Med. Chem. 13:477-523; Jeffrey et al (2006) Bioorganic & Med. Chem. Letters 16:358-362; Torgov et al (2005) Bioconj. Chem. 16:717-721; Nagy et al (2000) Proc. Natl. Acad. Sci. 97:829-834; Dubowchik et al (2002) Bioorg. & Med. Chem. Letters 12:1529-1532; King et al (2002) J. Med. Chem. 45:4336-4343; U.S. Pat. No. 6,630,579). The antibody-drug conjugate BR96-doxorubicin reacts specifically with the tumor-associated antigen Lewis-Y and has been evaluated in phase I and II studies (Saleh et al (2000) J. Clin. Oncology 18:2282-2292; Ajani et al (2000) Cancer Jour. 6:78-81; Tolcher et al (1999) J. Clin. Oncology 17:478-484).
Morpholino analogs of doxorubicin and daunorubicin, formed by cyclization on the glycoside amino group, have greater potency (Acton et al (1984) J. Med. Chem. 638-645; U.S. Pat. No. 4,464,529; U.S. Pat. No. 4,672,057; U.S. Pat. No. 5,304,687). Nemorubicin is a semisynthetic analog of doxorubicin with a 2-methoxymorpholino group on the glycoside amino of doxorubicin and has been under clinical evaluation (Grandi et al (1990) Cancer Treat. Rew. 17:133; Ripamonti et al (1992) Brit. J. Cancer 65:703;), including phase II/III trials for hepatocellular carcinoma (Sun et al (2003) Proceedings of the American Society for Clinical Oncology 22, Abs1448; Quintieri (2003) Proceedings of the American Association of Cancer Research, 44:1st Ed, Abs 4649; Pacciarini et al (2006) Jour. Clin. Oncology 24:14116)
Nemorubicin is named as (8S,10S)-6,8,11-trihydroxy-10-((2R,4S,5S,6S)-5-hydroxy-4-((S)-2-methoxymorpholino)-6-methyltetrahydro-2H-pyran-2-yloxy)-8-(2-hydroxyacetyl)-1-methoxy-7,8,9,10-tetrahydrotetracene-5,12-dione, with CAS Reg. No. 108852-90-0, and has the structure:

Several metabolites of nemorubicin (MMDX) from liver microsomes have been characterized, including PNU-159682, (Quintieri et al (2005) Clinical Cancer Research, 11(4):1608-1617; Beulz-Riche et al (2001) Fundamental & Clinical Pharmacology, 15(6):373-378; EP 0889898; WO 2004/082689; WO 2004/082579). PNU-159682 was remarkably more cytotoxic than nemorubicin and doxorubicin in vitro, and was effective in vivo tumor models. PNU-159682 (formula (IIA) is named as 3′-deamino-3″,4′-anhydro-[2″(S)-methoxy-3″(R)-oxy-4″-morpholinyl]doxorubicin, and has the structure:

Certain PNU-159682 antibody-drug conjugates have been described (“NEMORUBICIN METABOLITE AND ANALOG ANTIBODY-DRUG CONJUGATES AND METHODS”, PCT/US2009/031199, filed 16 Jan. 2009).